Power tools may be used in various assembly processes, including fastening of joints etc. When fastening joints it is important that fasteners of such joints are tightened such that required tightening force levels are reached.
In order to control the tightening force of joints, the elongation of the fastener may be monitored during fastening. A previous patent SE 533385 discloses a method and a tool for measuring elongation of a fastener with ultrasound. By measuring the elongation of the fastener, the tightening force of the fastener may be assessed.
However, there is always a need for improving such methods of measuring fasteners with ultrasound to be able to improve reliability and robustness of the measurements on elongation and thereby the reliability and robustness of measurements of the tightening force.